Circulation and reaction enhancement of mass transport in a cavity

We numerically examine the mass transport into a fluid in the classical dri ven cavity problem and in the limit of large Peclet number, Pe. The species absorbed into the fluid is allowed to undergo a simple first-order chemica l reaction. Two particular types of boundary conditions are imposed: a macr oscopic gradient between the bottom and top surface and a zero-flux conditi on. We demonstrate that, in the absence of a chemical reaction and when a m acroscopic gradient is present, mass transport into the liquid is enhanced due to a recirculation zone in the cavity which is connected to the top and bottom surfaces through two boundary layers. The corresponding enhancement is large and scales as Pe(1 2). In the presence of a chemical reaction wit h rate constant k, adsorption into the liquid is further enhanced with the flux at the top surface now scaling as k(1 2) for k much greater than Pe, H owever, for k = O(Pe), the chemical reaction removes the central spatially uniform concentration region from the cavity as well as the boundary laver at the bottom wall. (C) 2001 Elsevier Science Ltd. All rights reserved.